1. Technical Field
This disclosure relates to methods for providing a desired selectivity of oxide to nitride etchrate when forming a Self Aligned Contact (SAC) in a semiconductor device. More particularly, the selectivity of oxide to nitride etchrate is provided by depositing carbon into at least a portion of a nitride layer in the semiconductor device prior to etching.
2. Background of Related Art
Etching to form a Self Aligned Contact (SAC) on a semiconductor device is known. To produce a satisfactory SAC, a high etchrate selectivity of oxide to nitride is required. Unless adequate etchrate selectivity is provided, a well defined corner is not formed in the SAC and the semiconductor device is subject to failure and/or unreliability. Presently, corner selectivities of 20:1 can be achieved using a C.sub.4 F.sub.8 /CO/Ar chemistry to perform the etching. However, several disadvantages are associated with use of CO in the etch chemistry such as, for example, metal contamination and difficult handling. Unfortunately, removing CO from the etch chemistry results in poor corner selectivity and hence poor quality product.
It therefore would be desirable to provide a desired selectivity of oxide to nitride etchrate during SAC etching without the use of CO-containing chemistry.